In the medical field, an X-ray radiographing apparatus refers to an apparatus that radiates a predetermined amount X-rays toward a body part to be radiographed, senses the X-rays having passed therethrough by using an X-ray sensor, and reconstructs an X-ray image by using electrical signals sensed by the X-ray sensor. The X-rays having passed through the body part are attenuated in a rate varying according to substances in their travelling path and are transformed to electrical signals by the X-ray sensor by photoelectric. The X-ray radiographing apparatus provides information of interior of the radiographing target in an X-ray image by using electrical signals in which accumulated attenuation rate is reflected according to the X-ray travelling path.
In the field of dental diagnosing, CT images are widely used as the CT images accurately and clearly display a three-dimensional X-ray image of the teeth arrangement, temporomandibular joint or head of the patient, which are main parts of interest among body parts, and tomographic images according to the position and direction desired by the user. Accordingly, such images are used in fields requiring high precision such as implant treatment. An X-ray computed tomography (CT) radiographing apparatus reconstructs X-ray images of a radiographing target which are radiographed in various angles, and provides a three-dimensional X-ray image of the radiographing target. For this, the X-ray CT radiographing apparatus includes an X-ray generator, an X-ray sensor disposed to face the X-ray generator with a subject disposed therebetween, a rotation supporter rotating the X-ray generator and the X-ray sensor while supporting the same, and an image reconstructing unit implementing a CT image by using results sensed by the X-ray sensor.
In order to obtain an X-ray CT image, the X-ray generator and the X-ray sensor rotates facing each other within a predetermined angular range based on a rotation shaft passing through the radiographing target, and X-ray CT data of a field of view in various angles, that is a FOV, is obtained. When performing general X-ray CT radiographing, the X-ray generator and the X-ray sensor rotates around the central axis of the FOV as a rotating axis, and X-rays having passed the entire area of the FOV are received in various angles. Accordingly, for panoramic X-ray image radiographing, a large-size sensor is significantly larger than the X-ray sensor is required.
In one embodiment, describing a case of obtaining an X-ray CT image of a FOV having a first height t1 and a first width w1 by using an X-ray having a cone beam form which is widely used in the dental field, a second height t2 of a sensor has to be equal to or greater than magnification ratio*first height t1, the magnification ratio is defined as the ratio of the distance between the X-ray generator and the examinee to the distance between the X-ray generator and the X-ray sensor (t2≥magnification ratio*t1), and a second width w2 of the sensor has to be equal to or greater than magnification ratio*first width w1 (w2≥magnification ratio*w1) so that the sensor may receive X-rays having passed all areas of the FOV. Herein, if necessary, a method of using a half beam which downsizes the second width of the sensor up to maximum magnification ratio*(w1)/2 by using an X-ray beam covering ½ or more of the FOV. However, when using a half beam method in a conventional X-ray CT radiographing apparatus, a relatively large-size X-ray sensor is required. In addition, there is a problem that a relatively large amount of X-ray exposure is required.